carbohydrate and bacterial/viral infectionslwang/bcmb8020/carbo-pathogen-infection.… ·...

Carbohydrate and Bacterial/Viral Infections

! Introduction

! Bacterial surface glycans as virulence factors

! Mechanisms of carbohydrate in pathogen

colonization and invasion

! Glycans in viral infection

! Development of glycan–based therapeutic

strategies


! Infectious diseases remain a major cause of death, disability, and social

and economic disorder

!Multiple reasons contribute to the expanding impact of infectious

diseases

! Development of prevention and treatment strategies requires a well

understanding the interaction of viral or bacterial pathogen with human

!Glycans are major components of the outermost surface cells, including

animal, plant cells, bacteria and viruses

! The interactions of microbial pathogens with their hosts are influenced to

an important degree by the pattern of glycans and glycan-binding

receptors that each expresses-- all stages of infection: initial colonization,

spreading, induction of immunological response and/or host-cell injury.

!

Chapter 39, Figure 1

Classical experiments on the role of the pneumococcal polysaccharide capsule in virulence

Essentials of Glycobiology

Second Edition

Virulence Factor: Polysaccharide Capsule

! Virulence factor: the micobial molecules responsible for diseases manifestation

! Glycan–receptor interactions play crucial roles in microbial pattern recognition as well

as in the regulatory signals that govern the normal activities of immune cells. One

important reason why certain microbes cause disease is that they have evolved to

display their own sugars and receptors in a fashion that mimics or interferes with host

glycan-based immune functions

!The disease-causing bacteria share in common is the presence of a polysaccharide

capsule that covers the bacterial surface.

! Capsule expression by the bacteria poses a particular challenge to immune

clearance.

" Escape recognition and killing by phagocytes

" Directly bind host cell regulatory protein factor H, attenuating immune response

by hosts

" Cloak protein structures on their surfaces, escaping antibody-mediated killing

" Infants and elders generate poor antibody responses against bacterial

polysaccharide capsules, therefore, are particular prone to invasive infection of the

capsulated pathogen

! Molecular Mimicry: Strategy some microbial pathogens use to evade

immune recognition by decorating themselves with molecules structurally

similar to those of their hosts.

! Molecular mimicry of common host glycan structures, masking as “self” to

avoid immune recognition

- Group A Streptococcus express hyaluronan capsule

- Neisseria Meningitidis (meningococcus) express homopolymeric sialic

acid capsule

• group C meningococcal capsule : ! 2-9-linked sialic acid

polymer/unique bacterial structure/ be a successful vaccine antigen in

human

• group B meningococcal capsule : ! 2-8-linked sialic acid

polymer/found on human neural tissue/nonimmunogenic in human

Virulence Factor: Polysaccharide Capsule

! Different strains of the same bacterial species produce polysaccharide

capsules different in compositions and linkages of repeating sugar units.

!These structures are immunologically distinct, allowing classification of

different capsule “serotype” strains.

- Meningococcus : five major capsule serotypes (A, B, C, Y, and W-135)

- Haemophilus influenzae: six serotypes (A–F)

- Streptococcus pneumoniae (pneumococcus): > 90 serotypes

! Antibodies generated by the host against the capsule of one serotype

strain typically do not provide cross-protective immunity- a strategy to

present a moving target to the host immune system (keep escaping)

! Genetic exchange of capsule biosynthetic genes among serotype

strains of an individual species - capsule switching in vivo, escaping from

protective immunity.

Polysaccharide Capsule Structure

Virulence Factor: Lipopolysaccharide (LPS)

! LPS = endotoxin

! Major component of the outer membrane of Gram-

negative bacteria.

! LPS is a pathogen-associated molecular pattern (PAMP)

that is recognized by the innate immune system and

stimulates inflammatory responses to clear bacteria

! LPS interacts with the opsonic receptor CD14 and the

membrane protein Toll-like receptor 4 (TLR4) to initiate the

immune signaling process


Activation of immune signaling by LPS


Second Edition

! Dysregulated LPS-TLR4 interaction may lead to sepsis

! Gram-negative bacteria vary or modify their LPS to interfere

with host immune defense mechanisms

-Reduce overall negative charge to attenuate function of

cationic host antimicrobial peptides (Salmonella: addition

of 4-aminoarabinose to the phosphate group of the lipid A

backbone; Pseudomonas aeruginosa: synthesize a unique

hexa-acylated lipid A containing palmitate and 4-

aminoarabinose)

- temperature-modulated LPS structure change (e.g.

Yersinia pestis)

Virulence Factor: Lipopolysaccharide (LPS)

Virulence Factor: Lipooligosaccharide (LOS)

! Many mucosal pathogens such as H. influenzae and

Neisseria gonorrhoeae lack true O-antigens; instead, they

produce lipooligosaccharides (LOSs) that contain a

recognizable core structure from which one or more

monosaccharide or short oligosaccharide branches extend.

! LOS plays a pivotal role in infection

- structurally switch

- Induce local inflammatory response

- Resistance to bactericidal activity of serum

- Molecular mimicry: gonococcal LOS and

glycophingolipid antigens on human erythrocyte have

structural similarity.

Carbohydrate in Pathogen Colonization & Invasion

! Adhesin: A protein on the surface of bacteria, viruses, or parasites thatbinds to a ligand present on the surface of a host cell.

- most are lectins

- Interact with cell surface glycoproteins, glycosphingolipids, or glycosaminoglycans

- Alternatively interact with matrix or mucin

- The interactions are mediated through terminal sugars or internal carbohydrate motifs

! Adhesin receptor: The specific carbohydrate ligands that presnt on hostcell surface and mediate bacterial attachment on the host cell surface.

- quite diverse in nature

- The array of available adhesin-receptors determine the tropism of individual bacteria

! Pili: Hair-like appendages on the surface of some bacteria that often containadhesins.

- E. coli :P-blood group-related glycosphingolipids in the bladder epithelium

- Salmonella: adherence to human intestinal cell mucosa

! Fimbriae: Proteinaceous fiber-like appendages found in many Gram-negative bacteria

!Afimbrial adhesin: a surface-anchored protein expressed by the bacteria.- Hemagglutinin: a lectin that recognizes carbohydrates on the surface of red blood cells andcauses hemagglutination.

- Bordetella pertussis: Filamentous hemagglutinin (FHA) -strong attachment of the bacteria tothe ciliated epithelial cells of the bronchi and trachea, resulting “whooping cough”.- FHA is a component of pertussis vaccine.

!Two step epithelial attachment: carbohydrate of host is modified by pathogenand generates neostructure which mediates the pathogen adhesion.


Bacterial adherence to host-cell surfaces


Second Edition

Carbohydrates & Invasion Factors

! Glycan–lectin interactions play pivotal roles in enabling certain

pathogens to penetrate or invade through epithelial barriers.

- S. enterica : outer core oligosaccharide structure of the serovar Typhi

LPS mediates the bacteria internalization in epithelial cells.

- Streptococcus pyogenes: attaches to human pharyngeal and skin

epithelial cells through specific recognition of its hyaluronan capsular

polysaccharide by the hyaluronan-binding protein CD44, resulting cytoskeletal

rearrangements and opening of intercellular junction.

Carbohydrates & Biofilm

! Biofilm: Community of bacteria that adheres to a moist surface (e.g.,

surface of ponds or teeth)

!A mechanism that promotes bacterial attachment to host surfaces, often in a

form of a polymicrobial community.

!Oral films: - Streptococcus species predominate (60–90%).

- Dental plaque: dense, mushroom-like clumps of bacteria pop up from the

surface of the tooth enamel, interspersed with bacteria-free channels filled with

extracellular polysaccharide (EPS) produced by the bacteria.

!EPS: - Serve as diffusion channel-”quorum sensing”

- Physical barrier for host immune system and antibiotics

- Bind and inactivate antimicrobial peptides and antibiotics

- Synthesized by biofilm bacteria vary in composition, and in chemical and

physical properties.

Majority of EPS types are polyanionic:

Contributed by inorganic residues too.

- serve as the primary carbon reserve for biofilm microorganisms during

substrate deprivation


Structure of a polymicrobial biofilm


Second Edition

Heparan Sulfate in Pathogen Infection

! Heparan sulfate proteoglycan as attachment factors for host epithelia, such

as Chlamydia trachomatis and N. gonorrhoeae

! Heparan sulfate proteoglycan shedding from host cell surface, such as

Staphylococcus aureus and Pseudomonas aeruginosa. The negatively

charged heparan sulfate side chains of the shed ectodomain bind tightly to

cationic molecules such as antimicrobial defensin peptides and lysozyme,

neutralizing their antibacterial activities.

Carbohydrate & Viral Infection

! The specific binding of a virus particle to a target receptor on the

host-cell surface is a prerequisite for viral infection.

! Most viral receptors are mapped to the glycan components of cell-

surface glycoproteins, glycolipids, or proteoglycans

!The virus–glycan interactions are responsible for species and tissue

tropism

Influenza Virus

! Common pathogens of the upper respiratory tract.

! Seasonal epidemics affect 10–20% of the general population

! Can be deadly

! Influenza virus subtype is named based on their surface glycoprotein -

hemagglutinin (H) and neuraminidase (N)

-H1N1 - 1930s

-H2N2 - 1958

-H3N2 - 1968 - recent years

!Typically, human and avian influenza viruses are different and are not

infectious for both species.

Carbohydrate & Influenza Virus

! Interactions between influenza virus hemagglutinin and sialic acid

determine the tissue and species tropism of the virus.

-Human influenza viruses: terminal sialic acids containing ! 2-6 linkages

-Bird influenza viruses: terminal sialic acids containing ! 2-3 linkages

-Pig: ! 2-3- and ! 2-6-linked sialic acids occur in the trachea of swine

! The cell-surface receptor(s) for influenza viruses is widely considered to be

sialic acid linked to either glycoprotein or glycosphingolipid.

! Influenza virus enters cells may also depend on protein–glycan interactions

- host mannose receptors of macrophages

! The final release of influenza virus particles from an infected cell surface

relies on the action of the viral neuraminidase

! Neuraminidase may also assist pathogen in evading host mucosa


Mechanisms of viral entry into host cells


Second Edition

Herpes Simplex Virus (HSV)

! HSV1 & HSV2.

! Latent, recurrent infections

! HSV1 - recurrent cold sores of the mouth and lips

!HSV2 - sexually transmitted genital ulcer disease

!HSV infection is mediated by a family of ten viral

envelope glycoproteins.

-Initial attachment: HSV glycoprteins B (gB) and C

(gC) interact with heparan sulfate

- High-affinity attachment: glycoprotein D (gD)

interacts with a member of the tumor necrosis factor-

nerve growth factor receptor family




Second Edition

Human Immunodeficiency Virus (HIV)

! A retrovirus.

! The etiologic agent of the acquired

immunodeficiency syndrome (AIDS)

! The outer envelope glycoprotein gp120 is

responsible for the cellular tropism of the virus

! The transmembrane glycoprotein gp41

catalyzes fusion of HIV to the target cell’s

membrane

! The very heavy N-glycosylation of gp120/41

blocks immune response

! Heparan sulfate proteoglycans protect HIV

virion degradation in blood stream, function as an

attachment receptor for macrophage entry, and

transmit the viral particle in trans to CD4+ T cells.




Second Edition

Therapeutic Strategies Based on Microbial

Protein-glycan Interaction

! Influenza: Neuraminidase - sialic acid analogs (Zanamivir and

Oseltamivir)

! HIV: gp120 - high-mannose-type N-glycans attached (inhibitor of N-

glycosidation : N-buty-deoxyno-jirimycin).

! Cyanovirin-N: bind to the unusal oligomannose-type N-glycans presents on

gp120. Also against herpesviruses.

! Heparin and other polysulfated molecules.

! Carrageena: a polysulfated glycosaminoglycan-like extract from red

seaweed

! lectins and other carbohydrate-binding agents

! Anti-adhesion therapies: E. coli adhesion in urinary tract - ! -

methylmannoside or free mannose


! Introduction

! Bacterial surface glycans as virulence factors

! Mechanisms of carbohydrate in pathogen

colonization and invasion

! Glycans in viral infection

! Development of glycan–based therapeutic

strategies

carbohydrate and bacterial/viral infectionslwang/bcmb8020/carbo-pathogen-infection.… ·...

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